Figure 5.

Response histograms of MC on-center cell to 626/508 nm borders with differing luminance contrasts (average of 20 sweeps). In upper row and lower rows (A, B) the direction of chromatic contrast is reversed. The on-center cell shows an excitatory response to a luminance increment edge. To the equiluminant edge there is a response to both directions of chromatic contrast. Solid lines show fits of a Gaussian function. (C) Plot of chromatic vs. achromatic radius fit values. Most points can be seen to lie above the unity ratio line. Data are consistent with a chromatic response from a mechanism somewhat larger than the achromatic field center.